Electroplating



May 31, 1938. E. D. "VIERS ET AL 2,119,304

ELECTROPLATING Filed Aug. 1, 1955 2 sheetsI-sheet 1 lNVENTOR EUGENE D V/ERS V BERN/7RD C. 6455 ATTO RN EYS May 31, 1938. E. D. VIIERS ET AL 2,119,304

ELECTROPLATING Filed Aug. 1, 1935 2 Sheets-Sheet 2 Y IIJIVENTOR. EUGENE D. 105/25 BY BER/YARD C CASE ATTORNEYS' Patented May 3i, 1938 UNITED STATES 2,119,304 nnncmormme Eugene D. Viers and Bernard (3. Case, Cleveland,

Ohio, assignors to Eaton Detroit Metal-cmpany, Cleveland, Ohio, a coi'poration of Ohio 18 Claims.

l This invention relates to a commercial production of electroplates on metals and is particularly concerned with a method or a process for predicting and eliminating'the occurrence of pitting on the plate. For many years, little trouble was experienced in pitting during the electrodeposition of metal such as nickel on steel, copper and brass at low temperature and at low current density and high pH, for in the early period of commercial plating, a nickel surface that would buff to a nickel color was all that the trade required. Recently, however, particularly since nickel has been extensively used as a protective coating for automotive parts, it has become necessary to plate heavier deposits to withstand corrosion over longer periods of time. This'has necessitated an increase in current densities and other operating conditions to facilitate the deposition of nickel in the least pos- V sible time. For some time, copper was thought to be necessary as a base on which nickel should be plated, but only recently, experience has shown that copper as an alternate plate between nickel and steel did' not offer any protection for the base metal, but instead, contributed to the corrosion of either the steel ,or iron on account of its position in theelectromotive series with respect to iron. Consequently, copper has been eliminated and nickel has been plated directly upon the steel. Whilepitting became readily apparent when the current densities were increased, it became a serious commercial problem as soon as the intermediate copper plate was discontinued. We have made extensive researches into the origin of pits and we have established that there are many types and kinds of pits. For example, we have found that if an article is not properly cleaned or rinsed, it will retain small particles of foreign matter which'will cause a steady stream of hydrogen which will interfere with the deposition, and that pitting reslys whenever such articles of dirt interfer'ewvith the uniform release of hydrogen.

We have also found that pitting is formed when a deep abrasion or scratch is present on the surfaceof the base metal, as such occurrence also interferes with the normal evolution of,hydrogen during plating. Obviously, pitting which resulted from the foregoing conditions could be controlled upon proper treatment of the base metal, buteven when diligent efforts were made to correct such conditions, pitting was found to result when all of the other knowncauses were eliminated.

Application August 1, 1935, Serial No. 34,209

Microscopic studies of the nickel structure even ,under the most favorable conditions of plating revealed startling facts. For example, it was found that nickel plated upon copper had a finer grained structure than that placed upon steel. Again, nickel plated at high temperature 5 was coarser than that plated at low temperature and moreover nickel plated at high current densities was coarser than that plated at low current densities, but in every case, it was found that a finer grained, smoother surface would be substantially free from pits.

Commercial plating as heretofore practiced, has generally included the use of an addition agent, such as hydrogen peroxide, to the nickel bath for the alleged purpose of preventing pitting; and under such practices, the operator would replenish the tank at frequent-intervals approximately such for example as every two hours, with a certain quantity of the addition agent whichhad previously been discovered by the trial and error method as being necessary to prevent pitting in any particular tank. The difficulty with such procedure, however, has been that the repeated replenishment has not prevented pitting; that it has been expensive and that it has required attention at too frequent intervals for assurance of safety.

It has been assumed that hydrogen peroxide would eliminate the pitting at any depth, but we have found that regardlessof the amount 3 used, satisfactory commercial plating on steel beyond a depth of six ten thousandths of an inch could not be efiected, while satisfactory commercial plating on metals other than steel beyond a depth of one and one-fourth thousandths of an inch could not be obtained. 7

We have discovered that there is a definite relationship between pitting and grain size and that if the grain size is controlled, pitting can be eliminated. We have also discovered that even when hydrogen peroxide is used, the grain structure assumes the shape of an inverted cone with the apex end in contact with the base metal, and that such formation necessarily limits the depth of the plate, because as the depth increases, the base of the cone reaches a size that is beyond 'the limit of safe commercial plating. We have discovered that by the use of certain addition agents, the shape of the grain structure 50 can be modified so as to form a column of uniform cross sectional shape throughout its length and that by reason of such formation, the depth to which themetal can be plated, can be safely increased in production to one, and one-half 5 flve thousandths of an inch and still maintain a at the surface the grain size necessary to avoid pitting.

An object of our invention therefore, is to provide an indicator by means of which the conditions in a plating bath can be determined sufficiently far in advance to avoid loss by pitting. In this connection, our invention is concerned with a method of plating by means of which, the pitting can be eliminated regardless oi the depth of plate that is required for commercial production.

To illustrate the relationship between grain size and pitting, we have shown in Figs. 1 to 4, microphotographs which illustrate a gradual reduction in grain size of electrodeposited nickel; the grains being indicated at a, b, c, and d respectively. Fig. 5 is a cross sectional view on a greatly enlarged scale showing the grain structure of the nickel deposit on steel with the use of materials which have heretofore been known to the trade as addition agents to prevent pitting, while Fig. 6 is a similar cross sectional view showing ,the grain structure of a plate that is deposited in accordance with our invention.

It is well known that certain addition agents produce advantageous results in electroplating, but the function of the agents has not been fully understood, and no general rule has been known that would enable one to predetermine the type of agent that would produce the most beneficial results for a given set of conditions.

So far as we know, no one, heretofore, has ascertained that a definite relationship exists between grain size and pitting; moreover, although addition agents have been used, they have not permittednickel plating on steel to be accomplished at depths greaterthan six ten-thousandths-of an inch. Furthermore, the addition agents have not eliminated the necessity for constant supervision of bath conditions, and where hydrogen peroxide has been used, the cost has been an important factor in the operation of a plating plant.

Our invention is applicable for the plating of metals other than nickel, but by way of illustration, a satisfactory nickel bath is as follows:-

Oz. per gallon of solution NiSO4-7H2O 32 NiClz.6H2O 6 H3303 4 The pH of this bath can be adjusted between 2 to 5.8 and electrolyzed with a current density of 5 to 400 amps. per sq. ft. at temperatures which vary from room to boiling.

We have found that if the above-mentioned bath is used, for example, at. room temperature and with a current density of 5 amps. per sq. ft., the resulting grain structure .will be similar to tain addition agents ii added to the bath will not only eliminate pitting, but will also enable metal such as nickel, cadmium, cobalt, zinc and tin to be plated to depths which heretofore have been considered impractical for commercial work. Such addition agents may comprise any one of the following:-

' Grams per gallon Phenol in the proportions of 2% Naphtha-quinone do 1 Phenolphthalein do 1 /2 Where the term salt is used in the claims it is intended to include not only the addition of a salt per se, but also the addition of compounds which produce salts in the bath.

The phenol, naphtha-quinone and phenolphthalein may be grouped under a heading of chemicals which have a closed carbon chain.

In using the addition agents, we prefer to use the alkaline salts of the metals in alkaline plating baths, and we prefer to use the acid salts of the metals in neutral and acid plating baths. Furthermore, in using the metallic salts, we use a dissimilar metal for the addition agent from that metal which is to be plated in the bath. For example, in a nickel plating bath, we use any metallic salt mentioned other than that of nickel, and for cadmium, we use any metallic salt other than that of cadmium, etc.

The addition agents which we have mentioned have produced a very marked change in the grain formation. In Fig. 5, for example, in, indicates a base metal such as steel, and II indicates a layer of nickel that has been affixed to the steel by electrodeposition. The lines 12 leading upwardly from the base metal to the outer surface of the plate represent the grain formation of the plated metal when an addition agent, such as hydrogen peroxide, is used in the bath. The grain formation is similar to an inverted truncated cone and accordingly it will be apparent that as the thickness of the plate increases, the size of the grain at the surface increases. As the grain size increases to about five thousandths of a millimeter, pitting develops, and consequently satisfactory commercial plating of nickel on steel has not been accomplished in depths in excess of six ten thousandths of an inch; and so far as we know, pitting develops in the deposition of nickel at commercial rates on metals other than steel when the depth of plate exceeds one and a quarter thousandths of an inch.

By the use of addition agents which we have mentioned, we have modified the formation of the grain to that illustrated in Fig. 6, in which the lines I5 represent the grain formation in the plated metal. Such grains have uniform crosssectional columnar shape throughout their length and hence there is no limit of depth to which the metal can be plated in satisfactory commercial production. So long as addition agents are used in the proportions mentioned, the grain size will be approximately one thousandth of a millimeter 'and therefore entirely safe for commercial production.

To ascertain conditions in the bath, we examine a plated article, which is taken from the production line, either under a microscope and compare the grain size by observationwith plates of known' grain size, or we'measure the image on the ground glass plate of a microphotographic camera. So long as the grain size remains below five with water so as to maintain the desired level.

size and pitting, we have shown microphotographs in Figs. 1 and 2, in, which thegrain size is over eight thousandths of a millimeter; the

illustration in Fig. 1 being coarser than that of Fig. 2. In Fig.3, the grain size is approximately five thousandthsofa-millimeter, while in Fig. 4,

" the grain size is' approximately one thousandth of a millimeten, ;The article illustrated in Fig. 1

was foundto .be very badly pitted, while that in 'Fig. 2 hasaslight reduction in grain size with a corresponding.reduction,in the number of pits.

The article illustratediin Fig; 3 has agrain size in which verylittlepitting will occur, while that.

presented in Fig. 4 is well within therange of commercial plating and free from pits.

We have found when the grain size of grey nickel is controlled between one thousandth and five thousandths of a millimeter, that the articles will be accepted'commercially as being free from Gray nickel as referred to herein and as defined in the trade means-a plate which has a non-lustrous or non=image producing surface and is distinguished from brightplate which has a lustrous or image-producing surface. Bright nickel'plate has a grain size of approximately one ten-thousandth 'of a millimeter in which range pitting, due to grain size, does not occur.

,Our-i nvention possesses important commercial advantages for it has entirely eliminated pitting and yet, has'enabled metal to be plated on steel at depths heretofore considered impossible for commercial production. ,The invention is not limited to nickel plating, but is well adapted for dition agent is as follows:'

plating other materials such as cadmium, zinc and tin. In the case of'cadmium plating, a suitable bath prior to the'introduction of the ad- Oz. per gallon I 10 Cd(CN) 2 4.5 NaOH '7 In the case of zinc plating, a suitable bath prior to the introduction of the addition agent is as follows:-:

Oz. per gallon Zn(CN) 2 4 NaCN 3.5 NaOH 'r '7 NaF It is tobe understood that the pH of these various baths is adjusted, that they are electrolyzed at a current density similar to those used commercially, and that an addition agent mentioned is to be added in the proportion specified.

We claim:-'-

1. A continuous homogeneous ductile electrolytic deposit of gray nickel directly on steel wherein the deposit has a grain size between onethousandth and flve-thousandths of a millimeter and wherein the deposit exceeds six ten-thousandths ofan inch in thickness and is free of pitting.

2. A continuous homogeneous ductile electrolytic deposit. of gray nickel directly on steel wherein the deposit has a grain size between onethousandth and five-thousandths of a millimeter and wherein the grains have a substantially columnar' structure and wherein the deposit exceeds six ten-thousandths of an inch in thickness and is free of pitting.

3. A continuous homogeneous ductile electrolytic deposit of gray nickel on steel wherein. the deposit has a grain size between one-thousandth and five-thousandths of a millimeter and wherein the deposit exceeds six ten-thousandths of an inch and is free of pitting, and wherein the de- --bath an addition agent having the property of reducing the grainsize of the deposit in a sufficient quantity to restrict the grain size of the deposit to a value below that at which pitting, due to grain size, occurs, but above that of bright nickel, when the grain size approximates the upper limit stated.

4. An electroplating bath for the electro-deposition of a continuous homogeneous ductile gray deposit of nickel, substantially consisting of a solution of nickel sulphate, nickel chloride and boric acid, and an addition agent selected from the group consisting of a soluble salt of cadmium, zinc, tin, cobalt and lead in. the quantity of substantially two grams per gallon. I

5. A method of avoiding the occurrence of pitting in the electro-deposition of metals of the group consisting of nickel, zinc, cadmium, cobalt and tin, under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising maintaining in the bath an addition agent, having the property of reducing the grain size of the deposit, in a quantity suificient only to produce a deposit, the grain size of which is below, but substantially of the order of that at which pitting, due to grain size, occurs.

6. ,A method of avoiding the occurrence of pitting in the electro-deposition of gray nickel, under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising maintaining in the bath an addition agent, having the property of reducing the grain size of the deposit, in a suiiicient quantity to restrict the grain size of the deposit to a value below that at which pitting, due to grain size occurs, but above that of bright nickel.

7. A method of avoiding the'occurrence of pit ting in the electro-deposition of gray nickel under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising electrolyzing a bath at a current density in the neighborhood of 75 amperes per square foot of cathode surface or higher, maintaining in the bath an addition agent having the property of reducing the grain size of the deposit, in" a suflicient quantity to restrict the grain size oi. the deposit to a value below that at which pitting, due to grain size occurs, but above that of bright nickel.

8. A method of avoiding the occurrence of pitting in the electro-deposition' of gray nickel under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising maintaining in the bath an addition agent having the property of reducing the grain size of the deposit selected from a group consisting of a soluble salt of zinc, cadmium, cobalt, lead and tin in a suflicient quantity to restrict the grain size of the deposit to a value below that at which pitting, due to grain size occurs, but above that of bright nickel.

9. A method of avoiding the occurrence of pitting in the electro-deposition of zinc under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising maintaining in the bath an addition agent having the property of reducing the grain size of the deposit, said agent being an electrolyte soluble metal salt in a quantity suflicient only to produce a deposit, the grain size of which is below but substantially of the order of that at which pitting, due to grain size, occurs.

10. A method of avoiding the occurrence of pitting in the electro-deposition of tin under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising maintaining in the bath an addition agent having the property of reducing -the grain size of the deposit, said agent being an electrolyte soluble metal salt in a quantity sufiicient only to produce a deposit, the grain size of which is below but substantially of the order of that at which pitting, due to grain size, occurs.

11. A method of avoiding the occurrence of pitting in the electro-deposition of gray nickel under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising electrolyzing a bath at a cathode current density in the neighborhood of '75 amperes per square foot or over and maintaining in the bath an addition agent having the property of reducing the grain size of the deposit selected from the group consisting of a soluble salt of zinc, cadmium, cobalt, lead and tin in a sufficient quantity to restrict the grain size of the deposit to a value below that at which pitting, due to grain size, occurs but above that of bright nickel.

12. A method of avoiding the occurrence of pitting in the electro-deposition of gray nickel under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising maintaining in a sulphate bath an addition agent having a property of reducing the grain size of the deposit, selected from a group consisting of a soluble salt of zinc, cadmium, cobalt, lead and tin in a sufficient quantity to restrict the grain size of the deposit to a value below that at which pitting, due to grain size, occurs, but above that of bright nickel.

13. A method of avoiding the occurrence of pitting in the electro-deposition of zinc under con-' ditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising maintaining, in a cyanide bath, an addition agent having the property of reducing the grain size of the deposit, said agent being an electrolyte soluble metal salt in a quantity sufflcient only to produce a deposit, the grain size of which is below but substantially of the order of that at which pitting, due to grain size, occurs.

14. A method of avoiding the occurrence of pitting in the electro-deposition of tin under conditions which would otherwise normally produce a grain size growth at which pitting would occur, comprising maintaining in a stannate bath an addition agent having the property of reducing the grain size of the deposit, said agent being an electrolyte soluble metal salt in a quantity sufiicient only to produce a deposit, the grain size of which is below but substantially of the order of that at which pitting, due to grain size, occurs.

15. A method of avoiding the occurrence of pitting in the electro-deposition of gray nickel under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising electrolyzing a sulphate bath at a current density in the neighborhood of 75 amps. per square foot or over, and maintaining in the bath an addition agent having the property of reducing the grain size of the deposit selected from the group consisting of a soluble salt of zinc, cadmium, cobalt, lead and tin in a suflicient quantity to restrict the grain size of the deposit to a value below that at which pitting, due to grain size occurs, but above that of bright nickel. I

16. A method of avoiding the occurrence of pitting in the electro-deposition of gray nickel under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising maintaining in a sulphate bath which is adjusted to a pH of from 2 to 5.8 an addition agent having the property of reducing the grain size of the deposit and selected from a group consisting of a soluble salt of zinc, cadmium, cobalt, lead and tin in a sufficient quantity to restrict the grain size of the deposit to a value below that at which pitting, due to grain size occurs, but above that of bright nickel.

17. A method of avoiding the occurrence of pitting in the electro-deposition of gray nickel under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising maintaining in the bath an addition agent having the property of reducing the grain size of the deposit and selected from a. group consisting of a soluble salt of zinc, cadmium, cobalt, lead and tin and in a quantity of substantially two grams per gallon.

18. A method of avoiding the occurrence of pitting in the electro-deposition of gray nickel under conditions which otherwise would normally produce a grain size growth at which pitting would occur, comprising maintaining in the bath an addition agent having the property of reducing the grain size of the deposit, said agent being an electrolyte soluble metal salt in a quantity suflicient to restrict the grain size of the deposit to a value below that at which pitting, due to grain size, occurs. but above that of bright nickel.

EUGENE D. VIERS. BERNARD C. CASE.

7 CERTIFICATE OF CORRECTION. Petent- No. 2,119, 01 r Hey 51, 1958.

EUGENE D. VIERS, ET AL.

It is hereby certified that the above numbered patent was erroneouslj issued to "Eaton Detroit Metal Company" whereas said patent should have been issued to Eaton Manufacturing company, of Cleveland, Ohio, a corporation of Ohio, as assignee bymesne assignments, as shown by the record of assignments in this office; and finat the said Letters Patent should be read with this correction therein that the some may conform to the record of the case in the Patent Office.

Signed and sealed. this 9th day of August, A. D. 1958.

Leslie Frazer (Seal) Acting Commissioner of Pat 

